Cell Reproduction Chromosome Structure & Function

Review Nucleus: Control center of eukaryotic cells Contains genetic information Contains DNA in Chromosomes

Chromosome/Chromatin When a eukaryotic cell is not dividing, the DNA and associated proteins is a tangled mass of thin threads called chromatin. At the time of cell division, the chromatin condenses to form highly compacted structures called chromosomes. Chromatin chromosome

Histones DNA wraps tightly around histone proteins when coiling. DNA Supercoil

Chromosome/Chromatid Just prior to mitosis, each chromosome duplicates to form sister chromatids Sister chromatids are genetically identical. A duplicated chromosome is made of two sister chromatids held together in a region called the centromere.

When the cells divide sister chromatids separate from one another. At the end of mitosis, each chromosome consists of a single chromatid.

Chromosome Number Each species has a characteristic number of Chromosomes in their body cells: Humans: 46Cat: 38 Fruit fly: 8Catfish: 58 Broccoli: 18Dog: 78 Goldfish: 94Black Mulberry: 308 Mosquito: 6 King Crab: 208 Note: prokaryotes usually have only 1 chromosome

Sex chromosomes Chromosomes that determine sex. Chromosomes that determine sex. Humans: X or Y Humans: X or Y –Females: XX –Male: XY

Autosomes Chromosomes that do not determine sex

Homologous Chromosomes Every organism made by sexual reproduction haS 2 copies of each autosome. Every organism made by sexual reproduction haS 2 copies of each autosome. Same size and shape. Same size and shape. Carry genes for the same trait. Carry genes for the same trait.

Karyotypes A “picture” of a person’s 46 chromosomes. A “picture” of a person’s 46 chromosomes.

Karyotypes Chromosomes are arranged in homologous pairs.

Why use karyotypes? To determine sex: To determine sex: »Male- XY »Female- XX To see abnormalities in chromosomes To see abnormalities in chromosomes »Extra chromosomes »Missing chromosomes »Extra/missing pieces of chromosomes

Diploid Cells with two sets of chromosomes (both chromosomes for each homologous pair) & 2 sex chromosomes Cells with two sets of chromosomes (both chromosomes for each homologous pair) & 2 sex chromosomes 2n 2n

Haploid 1 set of chromosomes (1/2 as many as the diploid cell). 1 set of chromosomes (1/2 as many as the diploid cell). 1n 1n Sex cells Sex cells